Two-stage trigger procedure

ABSTRACT

The disclosure relates to a user equipment for being scheduled with uplink radio resources. The user equipment receives from a radio base station a first-stage uplink resource scheduling message, indicating uplink radio resources usable by the UE to perform an uplink transmission via an unlicensed cell. The receiver further receives a second-stage uplink resource scheduling message, which is related to the first-stage uplink resource scheduling message. Upon reception of the second-stage uplink resource scheduling message, a processor of the UE determines that an uplink transmission is scheduled in case the first-stage uplink resource scheduling message is valid. The first-stage uplink resource scheduling message is determined valid based on a determination as to whether an uplink transmission has been triggered by another second-stage uplink resource scheduling message within a predetermined time period prior to reception of the second-stage uplink resource scheduling message. The UE then performs an uplink transmission.

BACKGROUND Technical Field

The present disclosure relates to a user equipment for being scheduledwith uplink radio resources and to a method for operating the userequipment.

Description of the Related Art

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving a radioaccess technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and evolved UMTSTerrestrial Radio Access Network (UTRAN) is finalized as Release 8 (LTERel. 8). The LTE system represents efficient packet-based radio accessand radio access networks that provide full IP-based functionalitieswith low latency and low cost. In LTE, scalable multiple transmissionbandwidths are specified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0MHz, in order to achieve flexible system deployment using a givenspectrum. In the downlink, Orthogonal Frequency Division Multiplexing(OFDM)-based radio access was adopted because of its inherent immunityto multipath interference (MPI) due to a low symbol rate, the use of acyclic prefix (CP) and its affinity to different transmission bandwidtharrangements. Single-carrier frequency division multiple access(SC-FDMA)-based radio access was adopted in the uplink, sinceprovisioning of wide area coverage was prioritized over improvement inthe peak data rate considering the restricted transmit power of the userequipment (UE). Many key packet radio access techniques are employedincluding multiple-input multiple-output (MIMO) channel transmissiontechniques and a highly efficient control signaling structure isachieved in LTE Rel. 8/9.

LTE Architecture

The overall LTE architecture is shown in FIG. 1. The E-UTRAN consists ofan eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) andcontrol plane (RRC) protocol terminations towards the user equipment(UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control(MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP)layers that include the functionality of user-plane header compressionand encryption. It also offers Radio Resource Control (RRC)functionality corresponding to the control plane. It performs manyfunctions including radio resource management, admission control,scheduling, enforcement of negotiated uplink Quality of Service (QoS),cell information broadcast, ciphering/deciphering of user and controlplane data, and compression/decompression of downlink/uplink user planepacket headers. The eNodeBs are interconnected with each other by meansof the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relation betweenMMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user datapackets, while also acting as the mobility anchor for the user planeduring inter-eNodeB handovers and as the anchor for mobility between LTEand other 3GPP technologies (terminating S4 interface and relaying thetraffic between 2G/3G systems and PDN GW). For idle-state userequipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g., parameters of the IP bearerservice, or network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle-mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at the time ofintra-LTE handover involving Core Network (CN) node relocation. It isresponsible for authenticating the user (by interacting with the HSS).The Non-Access Stratum (NAS) signaling terminates at the MME, and it isalso responsible for the generation and allocation of temporaryidentities to user equipments. It checks the authorization of the userequipment to camp on the service provider's Public Land Mobile Network(PLMN) and enforces user equipment roaming restrictions. The MME is thetermination point in the network for ciphering/integrity protection forNAS signaling and handles the security key management. Lawfulinterception of signaling is also supported by the MME. The MME alsoprovides the control plane function for mobility between LTE and 2G/3Gaccess networks with the S3 interface terminating at the MME from theSGSN. The MME also terminates the S6a interface towards the home HSS forroaming user equipments.

Component Carrier Structure in LTE

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots as shown in FIG. 2, wherein the firstdownlink slot comprises the control channel region (PDCCH region) withinthe first OFDM symbols. Each subframe consists of a give number of OFDMsymbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release8)), wherein each OFDM symbol spans over the entire bandwidth of thecomponent carrier. The OFDM symbols thus each consist of a number ofmodulation symbols transmitted on respective subcarriers. In LTE, thetransmitted signal in each slot is described by a resource grid ofN_(RB) ^(DL)N_(sc) ^(RB) subcarriers and N_(symb) ^(DL) symbols. N_(RB)^(DL) is the number of resource blocks within the bandwidth. Thequantity N_(RB) ^(DL) depends on the downlink transmission bandwidthconfigured in the cell and shall fulfill N_(RB) ^(min,DL)≤N_(RB)^(DL)≤N_(RB) ^(max,DL), where N_(RB) ^(min,DL) and N_(RB) ^(max,DL)=110are respectively the smallest and the largest downlink bandwidths,supported by the current version of the specification. N_(sc) ^(RB) isthe number of subcarriers within one resource block. For normal cyclicprefix subframe structure, N_(sc) ^(RB)=12 and N_(symb) ^(DL)=7.

Assuming a multi-carrier communication system, e.g., employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block (PRB) is defined as consecutive OFDM symbolsin the time domain (e.g., 7 OFDM symbols) and consecutive subcarriers inthe frequency domain as exemplified in FIG. 2 (e.g., 12 subcarriers fora component carrier). In 3GPP LTE (Release 8), a physical resource blockthus consists of resource elements, corresponding to one slot in thetime domain and 180 kHz in the frequency domain (for further details onthe downlink resource grid, see for example 3GPP TS 36.211, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8)”, current version 12.6.0, section 6.2, availableat http://www.3gpp.org and incorporated herein by reference).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same consecutive subcarriers spanning a full subframeis called a “resource block pair”, or equivalent “RB pair” or “PRBpair”. The term “component carrier” refers to a combination of severalresource blocks in the frequency domain. In future releases of LTE, theterm “component carrier” is no longer used; instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources.

Similar assumptions for the component carrier structure will apply tolater releases too.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequencyspectrum for IMT-Advanced was decided, the actual available frequencybandwidth is different according to each region or country. Followingthe decision on the available frequency spectrum outline, however,standardization of a radio interface started in the 3rd GenerationPartnership Project (3GPP).

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers are aggregated inorder to support wider transmission bandwidths up to 100 MHz. Severalcells in the LTE system are aggregated into one wider channel in theLTE-Advanced system which is wide enough for 100 MHz even though thesecells in LTE may be in different frequency bands. All component carrierscan be configured to be LTE Rel. 8/9 compatible, at least when thebandwidth of a component carrier does not exceed the supported bandwidthof an LTE Rel. 8/9 cell. Not all component carriers aggregated by a userequipment may necessarily be Rel. 8/9 compatible. Existing mechanisms(e.g., barring) may be used to avoid Rel-8/9 user equipments to camp ona component carrier.

A user equipment may simultaneously receive or transmit on one ormultiple component carriers (corresponding to multiple serving cells)depending on its capabilities. An LTE-A Rel. 10 user equipment withreception and/or transmission capabilities for carrier aggregation cansimultaneously receive and/or transmit on multiple serving cells,whereas an LTE Rel. 8/9 user equipment can receive and transmit on asingle serving cell only, provided that the structure of the componentcarrier follows the Rel. 8/9 specifications.

Carrier aggregation is supported for both contiguous and non-contiguouscomponent carriers with each component carrier limited to a maximum of110 Resource Blocks in the frequency domain (using the 3GPP LTE (Release8/9) numerology).

It is possible to configure a 3GPP LTE-A (Release 10)-compatible userequipment to aggregate a different number of component carriersoriginating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may currently not be possible toconfigure a mobile terminal with more uplink component carriers thandownlink component carriers. In a typical TDD deployment the number ofcomponent carriers and the bandwidth of each component carrier in uplinkand downlink is the same. Component carriers originating from the sameeNodeB need not provide the same coverage.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time to preserve orthogonality of the subcarrierswith 15 kHz spacing. Depending on the aggregation scenario, then □ 300kHz spacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmission(s) needto be mapped on the same component carrier.

When carrier aggregation is configured, the mobile terminal only has oneRRC connection with the network. At RRC connectionestablishment/re-establishment, one cell provides the security input(one ECGI, one PCI and one ARFCN) and the non-access stratum mobilityinformation (e.g., TAI) similarly as in LTE Rel. 8/9. After RRCconnection establishment/re-establishment, the component carriercorresponding to that cell is referred to as the downlink Primary Cell(PCell). There is always one and only one downlink PCell (DL PCell) andone uplink PCell (UL PCell) configured per user equipment in connectedstate. Within the configured set of component carriers, other cells arereferred to as Secondary Cells (SCells); with carriers of the SCellbeing the Downlink Secondary Component Carrier (DL SCC) and UplinkSecondary Component Carrier (UL SCC). Maximum five serving cells,including the PCell, can be configured at the moment for one UE.

The configuration and reconfiguration, as well as addition and removal,of component carriers can be performed by RRC. Activation anddeactivation is done, e.g., via MAC control elements. At intra-LTEhandover, RRC can also add, remove, or reconfigure SCells for usage inthe target cell. When adding a new SCell, dedicated RRC signaling isused for sending the system information of the SCell, the informationbeing necessary for transmission/reception (similarly as in Rel-8/9 forhandover). Each SCell is configured with a serving cell index, when theSCell is added to one UE; PCell has always the serving cell index 0.

When a user equipment is configured with carrier aggregation there is atleast one pair of uplink and downlink component carriers that is alwaysactive. The downlink component carrier of that pair might be alsoreferred to as ‘DL anchor carrier’. Same applies also for the uplink.When carrier aggregation is configured, a user equipment may bescheduled on multiple component carriers simultaneously, but at most onerandom access procedure shall be ongoing at any time. Cross-carrierscheduling allows the PDCCH of a component carrier to schedule resourceson another component carrier. For this purpose a component carrieridentification field is introduced in the respective DCI (DownlinkControl Information) formats, called CIF.

A linking, established by RRC signaling, between uplink and downlinkcomponent carriers allows identifying the uplink component carrier forwhich the grant applies when there is no cross-carrier scheduling. Thelinkage of downlink component carriers to uplink component carrier doesnot necessarily need to be one to one. In other words, more than onedownlink component carrier can link to the same uplink componentcarrier. At the same time, a downlink component carrier can only link toone uplink component carrier.

Uplink/Downlink Scheduling

A MAC function in the eNodeB refers to scheduling, by which the eNBdistributes the available radio resources in one cell among the UEs andamong the radio bearers for each UE. In principle, the eNodeB allocatesthe downlink and uplink resources to each UE based on respectively thedownlink data buffered in the eNodeB and based on buffer status reports(BSRs) received from the UE. In this process, the eNodeB considers theQoS requirements of each configured radio bearer and selects the size ofthe MAC PDU.

The usual mode of scheduling is dynamic scheduling, by means of downlinkgrant/assignment messages (DCIs) for the allocation of downlinktransmission resources and uplink grant/assignment messages for theallocation of uplink transmission resources. They are transmitted on thephysical downlink control channel (PDCCH) using a cell radio networktemporary identifier (C-RNTI) to identify the intended UE. In additionto the dynamic scheduling, persistent scheduling is defined, whichenables radio resources to be semi-statically configured and allocatedto a UE for a longer time period than one subframe, thus avoiding theneed for specific downlink assignment messages or uplink grant messagesover the PDCCH for each subframe. For the configuration orreconfiguration of a persistent schedule, RRC signaling indicates theresource allocation interval at which the radio resources areperiodically assigned. When the PDCCH is used to configure orreconfigure a persistent schedule, it is necessary to distinguish thescheduling messages which apply to a persistent schedule from those usedfor dynamic scheduling. For this purpose, a special scheduling identityis used, known as the semi-persistent scheduling C-RNTI, SPS-C-RNTI,which for each UE is different from the C-RNTI used for dynamicscheduling messages.

In order to inform the scheduled users about their allocation status,transport format and other transmission-related information (e.g., HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.It should be noted that user allocation might also be performed on a TTI(Transmission Time Interval) basis, where the TTI length can be amultiple of the subframes. The TTI length may be fixed in a service areafor all users, may be different for different users, or may even bydynamic for each user. Generally, the L1/2 control signaling needs onlybe transmitted once per TTI. Without loss of generality, the followingassumes that a TTI is equivalent to one subframe.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which in most cases includes resource assignments andother control information for a mobile terminal or groups of UEs. Ingeneral, several PDCCHs can be transmitted in one subframe.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in their fields. Thedifferent DCI formats that are currently defined for LTE are describedin detail in 3GPP TS 36.212, “Multiplexing and channel coding”, section5.3.3.1 (current version v12.6.0 available at http://www.3gpp.org andincorporated herein by reference). For detailed information regardingthe DCI formats and the particular information that is transmitted inthe DCI, please refer to the mentioned technical standard or to LTE—TheUMTS Long Term Evolution—From Theory to Practice, Edited by StefanieSesia, Issam Toufik, Matthew Baker, Chapter 9.3, incorporated herein byreference. Additional formats may be defined in the future.

Layer 1/Layer 2 Control Signaling

In order to inform the scheduled users about their allocation status,transport format, and other transmission-related information (e.g., HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.It should be noted that user allocation might also be performed on a TTI(Transmission Time Interval) basis, where the TTI length can be amultiple of the subframes. The TTI length may be fixed in a service areafor all users, may be different for different users, or may even bydynamic for each user. Generally, the L1/2 control signaling needs onlybe transmitted once per TTI. Without loss of generality, the followingassumes that a TTI is equivalent to one subframe.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which in most cases includes resource assignments andother control information for a mobile terminal or groups of UEs. Ingeneral, several PDCCHs can be transmitted in one subframe.

It should be noted that in 3GPP LTE, assignments for uplink datatransmissions, also referred to as uplink scheduling grants or uplinkresource assignments, are also transmitted on the PDCCH. Furthermore,3GPP Release 11 introduced an EPDCCH that fulfills basically the samefunction as the PDCCH, i.e., conveys L1/L2 control signaling, eventhough the detailed transmission methods are different from the PDCCH.Further details can be found in the current versions of 3GPP TS 36.211and 36.213, incorporated herein by reference. Consequently, most itemsoutlined in the background and the embodiments apply to PDCCH as well asEPDCCH, or other means of conveying L1/L2 control signals, unlessspecifically noted.

Generally, the information sent in the L1/L2 control signaling forassigning uplink or downlink radio resources (particularly LTE(-A)Release 10) can be categorized to the following items:

-   -   User identity, indicating the user that is allocated. This is        typically included in the checksum by masking the CRC with the        user identity;    -   Resource allocation information, indicating the resources (e.g.,        Resource Blocks, RBs) on which a user is allocated.        Alternatively this information is termed resource block        assignment (RBA). Note, that the number of RBs on which a user        is allocated can be dynamic;    -   Carrier indicator, which is used if a control channel        transmitted on a first carrier assigns resources that concern a        second carrier, i.e., resources on a second carrier or resources        related to a second carrier; (cross carrier scheduling);    -   Modulation and coding scheme that determines the employed        modulation scheme and coding rate;    -   HARQ information, such as a new data indicator (NDI) and/or a        redundancy version (RV) that is particularly useful in        retransmissions of data packets or parts thereof;    -   Power control commands to adjust the transmit power of the        assigned uplink data or control information transmission;    -   Reference signal information such as the applied cyclic shift        and/or orthogonal cover code index, which are to be employed for        transmission or reception of reference signals related to the        assignment;    -   Uplink or downlink assignment index that is used to identify an        order of assignments, which is particularly useful in TDD        systems;    -   Hopping information, e.g., an indication whether and how to        apply resource hopping in order to increase the frequency        diversity;    -   CSI request, which is used to trigger the transmission of        channel state information in an assigned resource; and    -   Multi-cluster information, which is a flag used to indicate and        control whether the transmission occurs in a single cluster        (contiguous set of RBs) or in multiple clusters (at least two        non-contiguous sets of contiguous RBs). Multi-cluster allocation        has been introduced by 3GPP LTE-(A) Release 10.

It is to be noted that the above listing is non-exhaustive, and not allmentioned information items need to be present in each PDCCHtransmission depending on the DCI format that is used.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in their fields asmentioned above. In the following, some DCI formats are listed ascurrently defined for LTE. More detailed information is provided in the3GPP technical standard TS 36.212 v14.0.0, particularly in section5.3.3.1 “DCI formats”, incorporated herein by reference.

-   -   Format 0: DCI Format 0 is used for the transmission of resource        grants for the PUSCH, using single-antenna port transmissions in        uplink transmission mode 1 or 2.    -   Format 1: DCI Format 1 is used for the transmission of resource        assignments for single codeword PDSCH transmissions (downlink        transmission modes 1, 2 and 7).    -   Format 1A: DCI Format 1A is used for compact signaling of        resource assignments for single codeword PDSCH transmissions,        and for allocating a dedicated preamble signature to a mobile        terminal for contention-free random access (for all        transmissions modes).    -   Format 1B: DCI Format 1B is used for compact signaling of        resource assignments for PDSCH transmissions using closed loop        precoding with rank-1 transmission (downlink transmission mode        6). The information transmitted is the same as in Format 1A, but        with the addition of an indicator of the precoding vector        applied for the PDSCH transmission.    -   Format 1C: DCI Format 1C is used for very compact transmission        of PDSCH assignments. When format 1C is used, the PDSCH        transmission is constrained to using QPSK modulation. This is        used, for example, for signaling paging messages and broadcast        system information messages.    -   Format 1D: DCI Format 1D is used for compact signaling of        resource assignments for PDSCH transmission using multi-user        MIMO. The information transmitted is the same as in Format 1B,        but instead of one of the bits of the precoding vector        indicators, there is a single bit to indicate whether a power        offset is applied to the data symbols. This feature is needed to        show whether or not the transmission power is shared between two        UEs. Future versions of LTE may extend this to the case of power        sharing between larger numbers of UEs.    -   Format 2: DCI Format 2 is used for the transmission of resource        assignments for PDSCH for closed-loop MIMO operation        (transmission mode 4).    -   Format 2A: DCI Format 2A is used for the transmission of        resource assignments for PDSCH for open-loop MIMO operation. The        information transmitted is the same as for Format 2, except that        if the eNodeB has two transmit antenna ports, there is no        precoding information, and for four antenna ports two bits are        used to indicate the transmission rank (transmission mode 3).    -   Format 2B: Introduced in Release 9 and is used for the        transmission of resource assignments for PDSCH for dual-layer        beamforming (transmission mode 8).    -   Format 2C: Introduced in Release 10 and is used for the        transmission of resource assignments for PDSCH for closed-loop        single-user or multi-user MIMO operation with up to 8 layers        (transmission mode 9).    -   Format 2D: introduced in Release 11 and used for up to 8 layer        transmissions; mainly used for COMP (Cooperative Multipoint)        (transmission mode 10)    -   Format 3 and 3A: DCI formats 3 and 3A are used for the        transmission of power control commands for PUCCH and PUSCH with        2-bit or 1-bit power adjustments respectively. These DCI formats        contain individual power control commands for a group of UEs.    -   Format 4: DCI format 4 is used for the scheduling of the PUSCH,        using closed-loop spatial multiplexing transmissions in uplink        transmission mode 2.    -   Format 5: DCI format 5 is used for the scheduling of the PSCCH        (Physical Sidelink Control Channel), and also contains several        SCI format 0 fields used for the scheduling of the PSSCH        (Physical Sidelink Shared Control Channel). If the number of        information bits in DCI format 5 mapped onto a given search        space is less than the payload size of format 0 for scheduling        the same serving cell, zeros shall be appended to format 5 until        the payload size equals that of format 0 including any padding        bits appended to format 0.

LTE on Unlicensed Bands—Licensed-Assisted Access (LAA)

In September 2014, 3GPP initiated a new study item on LTE operation onunlicensed spectrum. The reason for extending LTE to unlicensed bands isthe ever-growing demand for wireless broadband data in conjunction withthe limited amount of licensed bands. The unlicensed spectrum thereforeis more and more considered by cellular operators as a complementarytool to augment their service offering. One advantage of LTE inunlicensed bands compared to relying on other radio access technologies(RAT) such as Wi-Fi is that complementing the LTE platform withunlicensed spectrum access enables operators and vendors to leverage theexisting or planned investments in LTE/EPC hardware in the radio andcore network.

However, it has to be taken into account that unlicensed spectrum accesscan never match the qualities of licensed spectrum access due to theinevitable coexistence with other radio access technologies (RATs) inthe unlicensed spectrum such as Wi-Fi. LTE operation on unlicensed bandswill therefore at least in the beginning be considered a complement toLTE on licensed spectrum rather than as stand-alone operation onunlicensed spectrum. Based on this assumption, 3GPP established the termLicensed Assisted Access (LAA) for the LTE operation on unlicensed bandsin conjunction with at least one licensed band. Future stand-aloneoperation of LTE on unlicensed spectrum, i.e., without being assisted bylicensed cells, however shall not be excluded. Enhanced LicensedAssisted Access (eLAA) is enhancement to LAA, particularly exploitingthe unlicensed spectrum in the uplink as well. Efficient use ofunlicensed spectrum as a complement to licensed spectrum has thepotential to bring great value to service providers, and, ultimately, tothe wireless industry as a whole. To leverage the full benefits of LTEoperation in unlicensed spectrum, it is of outmost importance to definea complete UL access scheme in addition to the already defined DL accessscheme.

The currently-intended general LAA approach at 3GPP is to make use ofthe already specified Rel-12 carrier aggregation (CA) framework as muchas possible, where the CA framework configuration as explained beforecomprises a so-called primary cell (PCell) carrier and one or moresecondary cell (SCell) carriers. CA supports in general bothself-scheduling of cells (scheduling information and user data aretransmitted on the same component carrier) and cross-carrier schedulingbetween cells (scheduling information in terms of PDCCH/EPDCCH and userdata in terms of PDSCH/PUSCH are transmitted on different componentcarriers).

A very basic scenario is illustrated in FIG. 4, with a licensed PCell,licensed SCell 1, and various unlicensed SCells 2, 3, and 4 (exemplarilydepicted as small cells). The transmission/reception network nodes ofunlicensed SCells 2, 3, and 4 could be remote radio heads managed by theeNB or could be nodes that are attached to the network but not managedby the eNB. For simplicity, the connection of these nodes to the eNB orto the network is not explicitly shown in the figure.

At present, the basic approach envisioned at 3GPP is that the PCell willbe operated on a licensed band while one or more SCells will be operatedon unlicensed bands. One benefit of this strategy is that the PCell canbe used for reliable transmission of control messages and user data withhigh quality of service (QoS) demands, such as for example voice andvideo, while an SCell on unlicensed spectrum might yield, depending onthe scenario, to some extent significant QoS reduction due to inevitablecoexistence with other RATs.

It has been agreed that the LAA will focus on unlicensed bands at 5 GHz.One of the most critical issues is therefore the coexistence with Wi-Fi(IEEE 802.11) systems operating at these unlicensed bands. In order tosupport fair coexistence between LTE and other technologies such asWi-Fi as well as to guarantee fairness between different LTE operatorsin the same unlicensed band, the channel access of LTE for unlicensedbands has to abide by certain sets of regulatory rules which may partlydepend on the geographical region and particular frequency band; acomprehensive description of the regulatory requirements for all regionsfor operation on unlicensed bands at 5 GHz is given in R1-144348,“Regulatory Requirements for Unlicensed Spectrum”, Alcatel-Lucent etal., RAN1 #78bis, September 2014 incorporated herein by reference aswell as the 3GPP Technical Report 36.889, current version 13.0.0.Depending on region and band, regulatory requirements that have to betaken into account when designing LAA procedures comprise DynamicFrequency Selection (DFS), Transmit Power Control (TPC), Listen BeforeTalk (LBT) and discontinuous transmission with limited maximumtransmission duration. The intention of 3GPP is to target a singleglobal framework for LAA which basically means that all requirements fordifferent regions and bands at 5 GHz have to be taken into account forthe system design.

For example, in Europe certain limits for the Nominal Channel Bandwidthis set, as apparent from section 4.3 of the European standard ETSI EN301 893, current version 1.8.1, incorporated herein by reference. TheNominal Channel Bandwidth is the widest band of frequencies, inclusiveof guard bands, assigned to a single channel. The Occupied ChannelBandwidth is the bandwidth containing 99% of the power of the signal. Adevice is permitted to operate in one or more adjacent or non-adjacentchannels simultaneously.

The listen-before-talk (LBT) procedure is defined as a mechanism bywhich an equipment applies a clear channel assessment (CCA) check beforeusing the channel. The CCA utilizes at least energy detection todetermine the presence or absence of other signals on a channel in orderto determine if a channel is occupied or clear, respectively. Europeanand Japanese regulations at the moment mandate the usage of LBT in theunlicensed bands. Apart from regulatory requirements, carrier sensingvia LBT is one way for fair sharing of the unlicensed spectrum and henceit is considered to be a vital feature for fair and friendly operationin the unlicensed spectrum in a single global solution framework.

In unlicensed spectrum, channel availability cannot always beguaranteed. In addition, certain regions such as Europe and Japanprohibit continuous transmissions and impose limits on the maximumduration of a transmission burst in the unlicensed spectrum. Hence,discontinuous transmission with limited maximum transmission duration isa required functionality for LAA. DFS is required for certain regionsand bands in order to detect interference from radar systems and toavoid co-channel operation with these systems. The intention isfurthermore to achieve a near-uniform loading of the spectrum. The DFSoperation and corresponding requirements are associated with amaster-slave principle. The master shall detect radar interference, canhowever rely on another device, associated with the master, to implementradar detection.

The operation on unlicensed bands at 5-GHz is in most regions limited torather low transmit power levels compared to the operation on licensedbands which results in small coverage areas. Even if the licensed andunlicensed carriers were to be transmitted with identical power, usuallythe unlicensed carrier in the 5 GHz band would be expected to support asmaller coverage area than a licensed cell in the 2 GHz band due toincreased path loss and shadowing effects for the signal. A furtherrequirement for certain regions and bands is the use of TPC in order toreduce the average level of interference caused for other devicesoperating on the same unlicensed band.

Detailed information can be found in the harmonized European standardETSI EN 301 893, current version 1.8.1, incorporated herein byreference.

Following this European regulation regarding LBT, devices have toperform a clear channel Assessment (CCA) before occupying the radiochannel with a data transmission. It is only allowed to initiate atransmission on the unlicensed channel after detecting the channel asfree based, e.g., on energy detection. In particular, the equipment hasto observe the channel for a certain minimum time (e.g., for Europe 20μs, see ETSI 301 893, under clause 4.8.3) during the CCA. The channel isconsidered occupied if the detected energy level exceeds a configuredCCA threshold (e.g., for Europe, −73 dBm/MHz, see ETSI 301 893, underclause 4.8.3), and conversely is considered to be free if the detectedpower level is below the configured CCA threshold. If the channel isdetermined as being occupied, it shall not transmit on that channelduring the next Fixed Frame Period. If the channel is classified asfree, the equipment is allowed to transmit immediately. The maximumtransmit duration is restricted in order to facilitate fair resourcesharing with other devices operating on the same band.

The energy detection for the CCA is performed over the whole channelbandwidth (e.g., 20 MHz in unlicensed bands at 5 GHz), which means thatthe reception power levels of all subcarriers of an LTE OFDM symbolwithin that channel contribute to the evaluated energy level at thedevice that performed the CCA.

In addition to the CCA described above, it might be required to apply anadditional extended CCA (ECCA) if the equipment is classified as LoadBased Equipment (LBE) according to the description in ETSI 301 893,clause 4.9.2.2, incorporated herein by reference. The ECCA comprises anadditional CCA observation time for the duration of a random factor Nmultiplied by a CCA observation time slot. N defines the number of clearidle slots resulting in a total idle period that has to be observedbefore initiating a transmission.

Furthermore, the total time during which an equipment has transmissionson a given carrier without re-evaluating the availability of thatcarrier (i.e., LBT/CCA) is defined as the Channel Occupancy Time (seeETSI 301 893, under clause 4.8.3.1). The Channel Occupancy Time shall bein the range of 1 ms to 10 ms, where the maximum Channel Occupancy Timecould be, e.g., 4 ms as currently defined for Europe. Furthermore, thereis a minimum Idle time the UE is not allowed to transmit after atransmission on the unlicensed cell, the minimum Idle time being atleast 5% of the Channel Occupancy Time. Towards the end of the IdlePeriod, the UE can perform a new CCA, and so on. This transmissionbehavior is schematically illustrated in FIG. 5, the figure being takenfrom ETSI EN 301 893 (there FIG. 2: “Example of timing for Frame BasedEquipment”).

FIG. 6 illustrates the timing between a Wi-Fi transmission and LAA UEtransmissions on a particular frequency band (unlicensed cell). As canbe seen from FIG. 5, after the Wi-Fi burst, a CCA gap is at leastnecessary before the eNB “reserves” the unlicensed cell by, e.g.,transmitting a reservation signal until the next subframe boundary.Then, the actual LAA DL burst is started. This would similarly apply toan LTE UE which after successfully performing the CCA, would reserve thesubframe by transmitting the reservation signal so as to then start theactual LAA UL burst.

Uplink Scheduling in Unlicensed Cells

DCI Formats 0A, 0B, 4A, and 4B are provided for eLAA so as to supportuplink transmissions (PUSCH) for single subframe and multiple subframegrants and respectively single and multiple antenna ports.

-   -   DCI Format 0A: Single subframe, single antenna port    -   DCI Format 0B: Multiple subframe, single antenna port    -   DCI Format 4A: Single subframe, multiple antenna ports    -   DCI Format 4B: Multiple subframe, multiple antenna ports

Details on these DCI format can be found in 3GPP technical standard TS36.212 v14.0.0, sections 5.3.3.1.1A, 5.3.3.1.1B, 5.3.3.1.8A, 5.3.3.1.8B,incorporated herein by reference.

Any of these DCI formats (i.e., Uplink grants) can be either asingle-stage grant or be part of a two-stage grant. In the currentexemplary implementations in LTE (see TS 36.212), this is reflected bythe “PUSCH trigger A”-field, which is a 1-bit field differentiatingwhether the received Uplink grant is for “a non-triggered scheduling”,when the bit value is 0 (i.e., single-stage uplink grant) or is for“triggered scheduling”, when the bit value is 1 (i.e., two-stage uplinkgrant). This can be controlled by the eNB, which is the responsibleradio network entity for the scheduling of radio resources to the UE.

The two-stage uplink scheduling procedure requires two separate messages(“Trigger A” and “Trigger B”) to be received in a specific manner by theUE so as to schedule one uplink transmission.

The trigger-A-message can be any of the above-noted uplink grants (i.e.,DCI Formats 0A, 0B, 4A, or 4B). In connection with this two-stage grant,the four DCI Formats include the following data fields, as presentlydefined in the technical standard TS 36.212 v14.0.0:

-   -   “PUSCH trigger A—1 bit, where value 0 indicates non-triggered        scheduling and value 1 indicates triggered scheduling as defined        in section 8.0 of [3].        -   Timing offset—4 bits as defined in [3].            -   When the flag for triggered scheduling is set to 0,                -   The field indicates the absolute timing offset for                    the PUSCH transmission.            -   Otherwise,                -   The first two bits of the field indicate the                    relative timing offset for the PUSCH transmission.                -   The last two bits of the field indicate the time                    window within which the scheduling of PUSCH via                    triggered scheduling is valid.”

In addition, the available DCI Formats for the trigger-A message alsoinclude the usual data fields for indicating the radio resources thatare scheduled for an uplink transmission, such as the “Resource blockassignment” field, the “modulation and coding scheme” field, “HARQprocess number” field, etc. Moreover, the DCI formats 0A, 0B, 4A, 4B(particularly the DCI CRC) can be scrambled with a UE specific identity(such as the C-RNTI), such that the corresponding uplink grants areaddressed to a specific UE.

The trigger-B-message has the DCI Format 1C as currently defined in TS36.212 v14.0.0, section 5.3.3.1.4, incorporated herein by reference. TheDCI Format 1C, as currently defined in the technical standard for usewithin the scope of unlicensed carrier transmissions, including atwo-stage grant procedure, is as follows:

“Else

-   -   Subframe configuration for LAA—4 bits as defined in section 13A        of [3]    -   Uplink transmission duration and offset indication—5 bits as        defined in section 13A of [3]. The field only applies to a UE        configured with uplink transmission on a LAA SCell    -   PUSCH trigger B—1 bit as defined in section 8.0 of [3]. The        field only applies to a UE configured with uplink transmission        on a LAA SCell    -   Reserved information bits are added until the size is equal to        that of format 1C used for very compact scheduling of one PDSCH        codeword”

The trigger B message (DCI Format 1C), when being used as describedabove as part of the two-stage grant procedure, is usually not addressedto a specific UE but rather a shared identity (in this case the CC-RNTI;Common Control RNTI, which is an RNTI to be used in the context ofproviding common control PDCCH information; see 3GPP TS 36.321 v14.0.0,incorporated herein by reference) can be used by the eNB to scramble theDCI Format 1C, particularly the CRC thereof.

The cross-reference “[3]” in the above citations of TS 36.212 refers tothe technical standard 3GPP TS 36.213, current version 14.0.0, of whichat least sections 8.0 and 13 are relevant to the two-stage grants andare thus incorporated herein by reference in their entirety.

Particularly, section 8 of TS 36.213 defines in great detail for an LAASCell when and how an uplink transmission (i.e., PUSCH) is to beperformed:

-   -   “For a serving cell that is a LAA SCell, a UE shall        -   upon detection of an PDCCH/EPDCCH with DCI format            0A/0B/4A/4B and with ‘PUSCH trigger A’ field set to ‘0’ in            subframe n intended for the UE, or        -   upon detection of PDCCH/EPDCCH with DCI format 0A/0B/4A/4B            and with ‘PUSCH trigger A’ field set to ‘1’ in the most            recent subframe from subframe n-v intended for the UE, and            upon detection of PDCCH with DCI CRC scrambled by CC-RNTI            and with ‘PUSCH trigger B’ field set to ‘1’ in subframe n    -   perform a corresponding PUSCH transmission, conditioned on the        channel access procedures described in clause 15.2.1, in        subframe(s) n+l+k+i with i=0, 1, . . . , N−1 according to the        PDCCH/EPDCCH and HARQ process ID mod(n_(HARQ_ID)+i,N_(HARQ)),        where    -   N=1 for DCI format 0A/4A, and value of N is determined by the        ‘number of scheduled subframes’ field in the corresponding DCI        format 0B/4B.        -   The UE is configured the maximum value of N by higher layer            parameter maxNumberOfSchedSubframes-Format0B for DCI format            0B and higher layer parameter            maxNumberOfSchedSubframes-Format4B for DCI format 4B;    -   value of k is determined by the scheduling delay field in the        corresponding DCI 0A/0B/4A/4B according to Table 8.2d if ‘PUSCH        trigger A’ field set to ‘0’ or Table 8.2e otherwise;    -   value of n_(HARQ_ID) is determined by the HARQ process number        field in the corresponding DCI format 0A/0B/4A/4B and        N_(HARQ)=16;    -   for ‘PUSCH trigger A’ field set to ‘0’ in the corresponding DCI        format 0A/0B/4A/4B,        -   l=4    -   otherwise    -   value of 1 is the UL offset as determined by the ‘UL        configuration for LAA’ field in the corresponding DCI with CRC        scrambled by CC-RNTI according to the procedure in subclause        13A, and ‘PUSCH trigger B’ field set to ‘1’,    -   value of v is determined by the validation duration field in the        corresponding PDCCH/EPDCCH with DCI format 0A/0B/4A/4B according        to Table 8.2f, and ‘PUSCH trigger A’ field set to ‘1’    -   the smallest value of l+k supported by the UE is included in the        UE-EUTRA-Capability

TABLE 8.2d k for DCI format 0A/0B/4A/4B with ‘PUSCH trigger A’ field setto ‘0’. Value of ‘scheduling delay’ field k 0000 0 0001 1 0010 2 0011 30100 4 0101 5 0110 6 0111 7 1000 8 1001 9 1010 10 1011 11 1100 12 110113 1110 14 1111 15

TABLE 8.2e k for DCI format 0A/0B/4A/4B with ‘PUSCH trigger A’ field setto ‘1’. Value of ‘scheduling delay’ field k 00 0 01 1 10 2 11 3

TABLE 8.2f ν for DCI format 0A/0B/4A/4B with ‘PUSCH trigger A’ field setto ‘1’. Value of ‘validation duration’ field v 00 8 01 12 10 16 11 20

The current 3GPP technical standards thus define in great detail how atwo-stage grant procedure is to be performed. It should be however notedthat the above provided definition of two-stage grant procedures ascurrently standardized is subject to a continuous change and improvementand thus may change in the future. Consequently, the above citedimplementation of the two-stage grant procedure according to the current3GPP technical standards is to be merely considered as an implementationexample, where many details are of less importance to the presentdisclosure.

Nevertheless, for the present disclosure it is assumed that the basicconcept behind the two-stage grant procedure will remain the same asdiscussed above. In particular, the basic concept will be explained inconnection with FIG. 7, which illustrates the functioning of a two-stagegrant including the transmission and reception of DCIs including triggerA and trigger B messages. For the following exemplary discussion it isassumed that the illustrated subframes are numbered by taking thesubframe at which the trigger B (i.e., the second stage uplinkscheduling message) is received in the UE, as reference subframe n; thepreceding and subsequent subframes are numbered accordingly. It isfurther assumed that the trigger A message is received at subframe n−3,and that a time window of length v is defined within which the two-stagegrant procedure can be validly performed. Put differently, the timewindow can be seen as defining the time period during which a trigger Bmessage can be received so as to actually trigger a corresponding uplinktransmission, based on the transmission parameters indicated by thetrigger A and/or trigger B messages.

The time window length v can exemplarily be indicated within the triggerA message, as exemplified above by the last 2 bits of the timing offsetfield of the DCI Formats 0A, 0B, 4A, 4B in TS 36.212 and Table 8.2.f ofTS 36.213.

When the trigger B message is received at subframe n, the UE willdetermine whether a related trigger A message was received by the UEwithin the time window of length v (starting immediately before thereception of the trigger B message, i.e., ranging from n−1 to n-v). Inthe illustrated scenario, the trigger A scheduling message was receivedin subframe n−3 and thus within the time window, thereby triggering theuplink transmission in the UE. The uplink transmission (i.e., PUSCH) isthen performed with a particular transmission timing offset at subframen+offset. The UE may perform the uplink transmission according to theinformation received in the trigger A message and trigger B message,e.g., using the indicated radio resources and modulation and codingscheme, etc.

The exact PUSCH timing offset is of less importance to the presentdisclosure. Exemplarily, as currently standardized in TS 36.213, thePUSCH timing offset is “l+k+i”, where the parameter l is defined by thetrigger B message (see “Uplink transmission duration and offsetindication” field of DCI Format 1C in TS 36.212 and Table 13A-2 of TS36.213), where the parameter k is defined by the trigger a message (seethe first 2 bits of the “Timing offset” field of any of the DCI Formats0A, 0B, 4A, and 4B in TS 36.212, as well as Table 8.2e in TS 36.213).Parameter i is applicable in case that multiple uplink subframes arescheduled by a two-stage uplink scheduling procedure, and in that caseis running from 0 to the number of granted subframes minus 1 (otherwiseit is just 0). More details can be derived from the above cited section8 of TS 36.213. However, the PUSCH timing offset for performing theuplink transmission according to this two-stage uplink schedulingprocedure may also be defined differently or may be even predetermined.

As mentioned above, 3GPP has defined a two-stage scheduling procedurefor uplink transmissions in unlicensed cells. This two-stage schedulingprocedure however can be further improved.

SUMMARY OF THE INVENTION

Non-limiting and exemplary embodiments provide improved methods and userequipments involved in scheduling uplink transmissions to be performedby the user equipments.

The independent claims provide non-limiting and exemplary embodiments.Advantageous embodiments are subject to the dependent claims.

According to one general aspect, a user equipment is described for beingscheduled with uplink radio resources. At least one cell is configuredfor communication between the user equipment and a radio base stationthat is responsible for scheduling uplink radio resources on the cell.The user equipment comprises a receiver that receives from the radiobase station a first-stage uplink resource scheduling message,indicating uplink radio resources usable by the user equipment toperform an uplink transmission via the scheduled cell. The receiverfurther receives from the radio base station a second-stage uplinkresource scheduling message, which is related to the first-stage uplinkresource scheduling message. The user equipment further comprises aprocessor that determines whether the first-stage uplink resourcescheduling message is valid or not. The processor determines, whenreceiving the second-stage uplink resource scheduling message, that anuplink transmission is scheduled in case the processor has determinedthat the first-stage uplink resource scheduling message is valid.Thereby, the determination if the first-stage uplink resource schedulingmessage is valid is based on a determination as to whether an uplinktransmission has been triggered by another second-stage uplink resourcescheduling message within a predetermined time period prior to receptionof the second-stage uplink resource scheduling message. The userequipment further comprises a transmitter that, in case the processorhas determined that an uplink transmission is scheduled, performs anuplink transmission via the scheduled cell. The cell can, for example,be an unlicensed cell in the context of 3GPP LTE Release 14, or anothercell where two-stage scheduling is supported.

Correspondingly, in another general aspect, the techniques disclosedhere feature a method for operating a user equipment for being scheduledwith uplink radio resources. At least one unlicensed cell is configuredfor communication between the user equipment and a radio base stationthat is responsible for scheduling uplink radio resources on theunlicensed cell. The method comprises receiving from the radio basestation a first-stage uplink resource scheduling message, indicatinguplink radio resources usable by the user equipment to perform an uplinktransmission via the unlicensed cell. The method further comprisesreceiving from the radio base station a second-stage uplink resourcescheduling message, which is related to the first-stage uplink resourcescheduling message. The method further comprises determining whether thefirst-stage uplink resource scheduling message is valid or not. Themethod further comprises determining, when receiving the second-stageuplink resource scheduling message, that an uplink transmission isscheduled in case it has been determined that the first-stage uplinkresource scheduling message is valid. Thereby, the determination if thefirst-stage uplink resource scheduling message is valid is based on adetermination as to whether an uplink transmission has been triggered byanother second-stage uplink resource scheduling message within apredetermined time period prior to reception of the second-stage uplinkresource scheduling message. The method further comprises performing anuplink transmission via the unlicensed cell, in case it has beendetermined that an uplink transmission is scheduled.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

These general and specific aspects may be implemented using a userequipment and a method, and a combination of user equipment and method.

BRIEF DESCRIPTION OF THE FIGURES

In the following exemplary embodiments are described in more detail withreference to the attached figures and drawings.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system,

FIG. 2 shows an exemplary downlink resource grid of a downlink slot of asubframe as defined for 3GPP LTE (Release 8/9),

FIG. 3 shows an exemplary uplink resource grid of an uplink slot of asubframe as defined for 3GPP LTE,

FIG. 4 illustrates an exemplary LAA scenario with several licensed andunlicensed cells,

FIG. 5 illustrates the transmission behavior for an LAA transmission,

FIG. 6 illustrates the timing between a Wi-Fi transmission and LAA UEdownlink burst for an unlicensed cell,

FIG. 7 exemplarily illustrates the two-stage uplink scheduling procedureas provided for uplink transmissions via unlicensed cells,

FIG. 8 illustrates multiple triggering of uplink transmissions in amulti-UE environment,

FIG. 9 illustrates prevention of multiple triggering of uplinktransmissions in a multi-UEs environment according to a firstimplementation of an embodiment,

FIG. 10 is a diagram for a two-stage uplink transmission procedureaccording to the first implementation of the embodiment,

FIG. 11 illustrates prevention of multiple triggering of uplinktransmissions in a multi-UEs environment according to a secondimplementation of the embodiment, and

FIG. 12 is a diagram for a two-stage uplink transmission procedureaccording to the second implementation of the embodiment.

DETAILED DESCRIPTION

A mobile station or mobile node or user terminal or user equipment is aphysical entity within a communication network. One node may haveseveral functional entities. A functional entity refers to a software orhardware module that implements and/or offers a predetermined set offunctions to other functional entities of a node or the network. Nodesmay have one or more interfaces that attach the node to a communicationfacility or medium over which nodes can communicate. Similarly, anetwork entity may have a logical interface attaching the functionalentity to a communication facility or medium over which it maycommunicate with other functional entities or correspondent nodes.

The term “radio resources” as used in the set of claims and in theapplication is to be broadly understood as referring to physical radioresources, such as time-frequency resources.

The term “unlicensed cell” or alternatively “unlicensed carrier” as usedin the set of claims and in the application is to be understood broadlyas a cell/carrier operated in an unlicensed frequency band, with aparticular frequency bandwidth. Correspondingly, the term “licensedcell” or alternatively “licensed carrier” as used in the set of claimsand in the application is to be understood broadly as a cell/carrieroperated in a licensed frequency band, with a particular frequencybandwidth. Exemplarily, these terms are to be understood in the contextof 3GPP as of Release 12/13 and the Licensed-Assisted Access Work Item.

FIG. 8 illustrates a UE that belongs to UE group #1, a UE that belongsto UE group #2, as well as an eNodeB.

It is assumed that a Trigger A, which is the first-stage uplink resourcescheduling message, is transmitted from the eNodeB to the UE of group #1at subframe n 2. In this exemplary case, the valid time window forTrigger A as sent to UE of group #1 is 5 subframes. Thereby, theinformation about the valid time window is provided by Trigger A itself.

It is further assumed that a Trigger B, which is the second-stage uplinkresource scheduling message, is transmitted from the eNodeB at subframen. Trigger B is received by both UEs of groups #1 and #2, although theeNodeB has transmitted Trigger B with the intention that same is thesecond-stage uplink resource scheduling message for the alreadytransmitted Trigger A (as the first-stage uplink resource schedulingmessage) to UE of group #1 at subframe n−2. In this exemplary case, itis assumed that no UE of group #2 has received any Trigger A within thecorresponding valid time window before Trigger B. Upon reception ofTrigger B, all UEs that are able to receive the Trigger B—whichgenerally includes UEs from group #1 as well as from group #2—need tocheck whether they had received a Trigger A within the correspondingvalid time window. Therefore, in this example, the UE of group #1 checksas to whether it has received a Trigger A up to 5 subframes earlier (inthis case, from subframe n−5 to subframe n−1). As Trigger A has beenreceived in subframe n−2, which is within the valid time window, the UEof group #1 will subsequently trigger an uplink transmission.

Since UE of group #2 has not received a Trigger A, Trigger B received atsubframe n will not trigger an uplink transmission by UE of group #2.

As further apparent from FIG. 8, UE of group #2 receives a Trigger A atsubframe n+1. In this exemplary case, the valid time window for TriggerA as sent to UE of group #2 is 3 subframes. As further shown in thisfigure, a second Trigger B is transmitted from the eNodeB (at subframen+3). The second Trigger B is again received by both UEs of groups #1and #2, although the eNodeB has transmitted the second Trigger B withthe intention that same is the second-stage uplink resource schedulingmessage for the Trigger A (as the first-stage uplink resource schedulingmessage) transmitted to the UE of group #2 at subframe n+1. Uponreception of Trigger B, UE of group #2 checks as to whether it hasreceived a Trigger A up to 3 subframes earlier (in this case, fromsubframe n to subframe n+2). As the corresponding Trigger A has beenreceived in subframe n+1, which is within the valid time window, the UEof group #2 will subsequently trigger an uplink transmission.

However, since the second Trigger B is also received at UE of group #1at subframe n+3, UE of group #1 will again check as to whether it hasreceived a Trigger A up to 5 subframes earlier (in this case, fromsubframe n−2 to subframe n+2). Considering that UE of group #1 hasreceived Trigger A at subframe n−2, that is, still within the valid timewindow for that received Trigger A, the UE of group #1 will againtrigger its second uplink transmission, although the second triggereduplink transmission was not intended by the eNodeB to be carried out byUE of group #1, but rather only by UE of group #2. According to thisexemplary scenario as shown in FIG. 8, such a second triggered uplinktransmission carried out by UE of group #1 would also occur, if thesecond Trigger B would be received at subframe n+2 (instead of receivedat subframe n+3). Only, if the second Trigger B would be received atsubframe n+4 or later, no multiple triggering of the uplink transmissionwould occur, considering the exemplary valid time window of 5 subframesfor UE of group #1.

Overall, such multiple triggering of an uplink transmission is notdesired in an multi-UE environment. A first reason is that such anundesired uplink transmission bears the risk of creating interference toother transmissions in the corresponding subframe. A second reason isthat such multiple triggering could imply a conflict of ULtransmissions: if the UE of group #1 is triggered an UL transmission bya Trigger B in subframe n, where the corresponding UL transmission wasindicated by Trigger A as lasting for 4 subframes, the corresponding ULtransmission exemplarily occurs in subframes n+2 to n+5. If the same UEof group #1 is again triggered an UL transmission by a Trigger B insubframe n+3, where again the corresponding UL transmission indicated bythe same Trigger A should be lasting for 4 subframes, the correspondingUL transmission exemplarily occurs in subframes n+5 to n+8. As can beseen, these two triggers would therefore cause a conflict for subframen+5, where it is not clear whether data is to be transmitted as a resultof the first trigger B or as a result of the second trigger B—eventhough the transmission resources may be identical in both cases, thecorresponding data will generally contain different transport blocks orpackets. Such a conflict should be avoided because it causes potentialfor misunderstanding between UE and eNodeB.

The following exemplary embodiments are conceived by the inventors tomitigate one or more of the problems explained above.

Particular implementations of the various embodiments are to beimplemented in the wide specification as given by the 3GPP standards andexplained partly in the background section, with the particular keyfeatures being added as explained in the following pertaining to thevarious implementations of the presented embodiment. It should be notedthat the embodiment may be advantageously used for example in a mobilecommunication system, such as 3GPP LTE-A (Release 10/11/12/13 and later)communication systems as described in the Technical Background sectionabove, but the embodiments are not limited to its use in theseparticular exemplary communication networks.

The explanations should not be understood as limiting the scope of thedisclosure, but as a mere example of embodiments to better understandthe present disclosure. A skilled person is aware that the generalprinciples of the present disclosure as generally outlined in the set ofclaims and in the explanations given in the summary section of thedescription can be applied to different scenarios and in ways that arenot explicitly described in the following. For illustration andexplanation purposes, several assumptions are made which however shallnot unduly restrict the scope of the following embodiments.

Furthermore, as mentioned above, the following embodiments may beimplemented in the 3GPP LTE-A (Rel. 12/13 and later) environment. Thevarious embodiments mainly allow for having an improved uplinktransmission scheme. Other functionality (i.e., functionality notchanged by the various embodiments) however may remain exactly the sameas explained in the background section or may be changed without anyconsequences to the various embodiments; for instance functions andprocedures defining how the uplink transmission is actually performed(e.g., segmentation, modulation, coding, beamforming, multiplexing) andscheduled (PDCCH, DCI, cross carrier scheduling, self-scheduling) or howthe usual uplink transmission timing by using the timing advanceprocedure is performed (e.g., initial timing advance, timing advanceupdate commands).

In the following, a general embodiment is described for solving theabove problem(s) in detail, which will be explained by using thefollowing exemplary scenario, devised to easily explain the principlesof the embodiment. The principles however can also be applied to otherscenarios, some of which will be explicitly mentioned in the following.

A UE starts a two-stage uplink resource scheduling. In particular, theresource scheduling is initiated by a first-stage uplink resourcescheduling message (Trigger A) for an unlicensed cell, which is receivedby a receiver of the UE. Subsequently, a second-stage uplink resourcescheduling message (Trigger B) for the unlicensed cell is received bythe receiver of the UE.

Subsequently, a processor of the UE determines whether the first-stageuplink resource scheduling message (Trigger A) is valid or not in afirst-stage uplink resource scheduling message validation. Thereby, thedetermination of the validity of this first-stage uplink resourcescheduling message (Trigger A) is based on a determination as to whetheran uplink transmission has been triggered by another second-stage uplinkresource scheduling message (Trigger B) within a predetermined timeperiod prior to reception of the second-stage uplink resource schedulingmessage (Trigger B).

Subsequently, it is determined by the processor, when receiving thesecond-stage uplink resource scheduling message (Trigger B), that anuplink transmission is scheduled in case the processor has determinedthat the first-stage uplink resource scheduling message (Trigger A) isvalid.

Finally, in case the processor has determined that an uplinktransmission is scheduled, a transmitter of the UE performs an uplinktransmission via the unlicensed cell.

This main principle of the disclosure as described above advantageouslyallows preventing of multiple uplink transmission triggering in amulti-UE environment. Since there is no risk for unintentionallytriggering, by a Trigger B that was intended for a different UE, asecond uplink transmission by that particular UE that has alreadypreviously triggered an uplink transmission within the valid timewindow, the eNodeB can directly transmit a new Trigger A to differentUEs right after having sent a Trigger B, even within the predeterminedtime period/valid time window.

By this means, the user/cell throughput can be improved significantly.Moreover, avoiding a multiple uplink transmission triggering, therequired Trigger A overhead can be reduced, since longer validity timesas indicated by Trigger A, can be used more efficiently.

In addition, a false alarm of a second Trigger B after a correct firstTrigger B within the validity time/valid time window does not cause afalse PUSCH transmission. This advantageously avoids error cases due tofalse alarm Trigger B.

FIG. 9 illustrates a first implementation of the embodiment whereinmultiple triggering of uplink transmissions in a multi-UEs environmentis prevented.

FIG. 9 basically illustrates the situation as already described above inconnection with FIG. 8 with respect to the reception of the triggers atthe UEs of groups #1 and #2. As discussed, UE of group #1 receives aTrigger B at subframe n+3. In order to avoid a second triggering of anuplink transmission (which would occur in a conventional system asdescribed in connection with FIG. 8), UE of group #1 checks as towhether another Trigger B has already triggered an uplink transmissionin a predetermined time period prior to reception of the Trigger B asreceived at subframe n+3. Preferably the predetermined time period isthe valid time window as indicated in the Trigger A message. In theexample, the predetermined time period is the valid time window of alength of 5 subframes (as already explained in connection with FIG. 8,where Trigger A notifies the UE about the number of subframes (v=5)which denotes the valid time window).

Hence, UE of group #1 checks as to whether another Trigger B hastriggered an uplink transmission within a time period of 5 subframesprior to subframe n+3. In particular, UE of group #1 checks as towhether another Trigger B has triggered an uplink transmission betweensubframe n−2 and n+2. As illustrated in FIG. 8, an uplink transmissionhas already been triggered by Trigger B received in subframe n. Hence,in order to avoid a multiple triggering of an uplink transmission withinthe valid time window for Trigger A, for any Trigger B received afterthe first Trigger B, which in the example is received in subframe n, theUE disregards Trigger A received at subframe n−2 which would create thevalid time window between subframe n−2 and n+2 and which would enableTrigger B received at subframe n+3 to trigger another uplinktransmission. In particular, disregarding Trigger A, which was receivedat subframe n−2, then avoids that Trigger B received at subframe n+3would trigger an uplink transmission, since no valid time window thenwould be found prior to the reception of Trigger B at subframe n+3. Itis to be noted that the expression “disregarding Trigger A” in case ofhaving found a previous uplink transmission triggered within the validtime window for such Trigger A means that Trigger A received at subframen−2 is “not considered” for Trigger B received at subframe n+3.

As a consequence, and as illustrated in FIG. 9, no undesiredsecond/multiple uplink transmission is triggered at subframe n+3 by UEof group #1. Hence, in this case only UE of group #2 triggers an uplinktransmission by the received Trigger B at subframe n+3. By means of thesolution, multiple triggering in the multi-UE environment isavoided/prevented.

FIG. 10 is a diagram for a two-stage uplink transmission procedureaccording to the first implementation of the embodiment as alreadymentioned above in connection with FIG. 9.

In step S101, a UE (either one of UEs of groups #1 and #2) starts atwo-stage uplink resource scheduling. In particular, the resourcescheduling is initiated by a first-stage uplink resource schedulingmessage for an unlicensed cell, which is received by the UE in stepS102. Subsequently, a second-stage uplink resource scheduling message isreceived by the UE for the unlicensed cell in step S103.

The first stage uplink resource scheduling message validation consistsof step S104, wherein it is determined as to whether an uplinktransmission has already been triggered by another second-stage uplinkresource scheduling message with in time period T prior to reception ofthe second-stage uplink resource scheduling message. Thereby, the “timeperiod T” corresponds to the “predetermined time period prior toreception of the second-stage uplink resource scheduling message” asreflected in the claims, as well as corresponds to the “valid timewindow” as shown in FIGS. 8 and 9.

If it has been determined that another uplink transmission has alreadybeen carried out within time period T (“Yes” in step S104), the processproceeds with step S102 with the next cycle of waiting for a first-stageuplink resource scheduling message.

If it is, however, determined in step S104 that no other uplinktransmission has been carried out within the time period T (“No” in stepS104), the process proceeds with step S105, which relates to determiningthat the first-stage uplink resource scheduling message is valid.

As the first-stage uplink resource scheduling message is valid, theprocess proceeds with step S106, which relates to scheduling uplinktransmission. Subsequently, in step S107, the uplink transmission isactually performed.

FIG. 11 illustrates a second implementation of the embodiment whereinmultiple triggering of uplink transmissions in a multi-UEs environmentis prevented. The second implementation is an alternative to the firstimplementation, wherein, however, a multiple triggering of an uplinktransmission by the same UE within the valid time window for Trigger Ais avoided by invalidating Trigger A instead of merely disregardingTrigger A as described in the first implementation.

Reference is made to the scenario of FIG. 9, wherein the second TriggerB has been received by UE of group #1 at subframe n+3. As an alternativeto the first implementation of the embodiment, in the secondimplementation of the embodiment according to FIG. 11, UE of group #1can actively invalidate Trigger A (which has been received at subframen−2), upon receiving Trigger B at subframe n (invalidation can also beperformed at subframe n+1 or n+2, but needs to be performed beforeinterpreting/analyzing/considering the second Trigger B at subframen+3). Hence, the second Trigger B as received at subframe n+3 is notable to trigger an uplink transmission at the UE of group #1, sincethere is no valid time window for Trigger A anymore. In other words, thesecond implementation of the embodiment actively disables/invalidatesTrigger A upon the reception of the first Trigger B (or at least priorto the reception of the next Trigger B), which has already triggered anuplink transmission. Hence, by actively invalidating/disabling TriggerA, thereby removing a valid time window for Trigger A, no unintendedmultiple uplink transmission can be triggered by UE of group #1.

Overall, it is to be noted that the second implementation of theembodiment (according to FIG. 11) generally differs from the firstimplementation (according to FIGS. 9 and 10) by invalidating Trigger A(removing the valid time window for Trigger A) upon an uplinktransmission having been triggered by the Trigger B, instead of merelydisregarding Trigger A (disregarding the valid time window for TriggerA) upon reception of a second Trigger B, as shown in FIG. 9.

Actively “invalidating/disabling Trigger A” may, for instance, beimplemented by toggling a specific bit in a field that is associatedwith invalidating/disabling of the first stage uplink transmissionresource scheduling message Trigger A.

FIG. 12 is a diagram for a two-stage uplink transmission procedureaccording to the second implementation of the embodiment as alreadymentioned above in connection with FIG. 11.

In step S101, a UE (either one of UEs of groups #1 and #2) starts atwo-stage uplink resource scheduling. In particular, the resourcescheduling is initiated by a first-stage uplink resource schedulingmessage for an unlicensed cell, which is received by the UE in stepS102. Subsequently, a second-stage uplink resource scheduling message isreceived by the UE for the unlicensed cell in step S103.

The first stage uplink resource scheduling message validation consistsof step S108, wherein it is determined as to whether the first-stageuplink resource scheduling message has been invalidated. If it isdetermined that the first-stage uplink resource scheduling message hasbeen invalidated (“Yes” in step S108), the process proceeds with stepS102 with the next cycle of waiting for a first-stage uplink resourcescheduling message or to step S103 waiting for a second-stage uplinkresource scheduling message.

If it is determined in step S108 that the first-stage uplink resourcescheduling message has not been invalidated (“No” in step S108), theprocess proceeds with step S105, which relates to determining that thefirst-stage uplink resource scheduling message is valid. Subsequently,as the first-stage uplink resource scheduling message is valid, theprocess proceeds with step S106, which relates to scheduling uplinktransmission. Subsequently, in step S107, the uplink transmission isactually performed. Thereafter, the process proceeds with step S109,which relates to invalidating the first-stage uplink resource schedulingmessage. Subsequently, the process proceeds with step S102 with the nextcycle of waiting for a first-stage uplink resource scheduling message orto step S103 waiting for a second-stage uplink resource schedulingmessage.

Should, for instance, a second-stage uplink resource scheduling messagebe received after the invalidation of the first-stage uplink resourcescheduling message (in step S109), the process proceeds from step S103to step S108. At step S108, it is determined that the first-stage uplinkresource scheduling message is invalid so that the process againproceeds to step S102 or step S103, without performing an uplinktransmission.

This procedure as described above reflects the specific behavior asillustrated in FIG. 11, where the second Trigger B at subframe n+3 doesnot initiate a further uplink transmission, since Trigger A has alreadybeen invalidated upon the first Trigger B has triggered the uplinktransmission.

In the foregoing description of the embodiment, a two-stage uplink radioresource scheduling is described for a cell of a communication system.It is to be noted that such the two-stage uplink radio resourcescheduling is not only possible for unlicensed or licensed cells, butalso for any cells that support a two-stage uplink radio resourcescheduling.

According to a further embodiment, which is implemented in theenvironment of Standard TS 36.213, clause 8.0, is proposed to specify inthe standard:

-   -   For a serving cell that is a LAA SCell, a UE shall        -   upon detection of an PDCCH/EPDCCH with DCI format            0A/0B/4A/4B and with ‘PUSCH trigger A’ field set to ‘0’ in            subframe n intended for the UE, or        -   upon detection of PDCCH/EPDCCH with DCI format 0A/0B/4A/4B            and with ‘PUSCH trigger A’ field set to ‘1’ in the most            recent subframe from subframe n-v intended for the UE that            has not been triggered by a ‘PUSCH trigger B’ field set to            ‘1’ within subframe n-v+1 and subframe n−1, and upon            detection of PDCCH with DCI CRC scrambled by CC-RNTI and            with ‘PUSCH trigger B’ field set to ‘1’ in subframe n    -   perform a corresponding PUSCH transmission, conditioned on the        channel access procedures described in clause 15.2.1, in        subframe(s) n+l+k+i with i=0, 1, . . . N−1 according to the        PDCCH/EPDCCH and [ . . . ]        Hardware and Software Implementation of the Present Disclosure

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware, software, or software incooperation with hardware. In this connection a user terminal (mobileterminal) and an eNodeB (base station) are provided. The user terminaland base station is adapted to perform the methods described herein,including corresponding entities to participate appropriately in themethods, such as receiver, transmitter, processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may for example be general purpose processors, digital signalprocessors (DSP), application specific integrated circuits (ASIC), fieldprogrammable gate arrays (FPGA) or other programmable logic devices,etc. The various embodiments may also be performed or embodied by acombination of these devices. In particular, each functional block usedin the description of each embodiment described above can be realized byan LSI as an integrated circuit. They may be individually formed aschips, or one chip may be formed so as to include a part or all of thefunctional blocks. They may include a data input and output coupledthereto. The LSI here may be referred to as an IC, a system LSI, a superLSI, or an ultra LSI depending on a difference in the degree ofintegration. However, the technique of implementing an integratedcircuit is not limited to the LSI and may be realized by using adedicated circuit or a general-purpose processor. In addition, a FPGA(Field Programmable Gate Array) that can be programmed after themanufacture of the LSI or a reconfigurable processor in which theconnections and the settings of circuits cells disposed inside the LSIcan be reconfigured may be used.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It shouldbe further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A user equipment comprising: a receiver,which in operation, receives from a radio base station a first-stageuplink resource scheduling message, which indicates uplink radioresources usable by the user equipment to perform an uplink transmissionvia an unlicensed cell, wherein the receiver, in operation, receivesfrom the radio base station a second-stage uplink resource schedulingmessage, which is related to the first-stage uplink resource schedulingmessage, a processor, which in operation, determines that thefirst-stage uplink resource scheduling message is valid when the uplinktransmission has not been triggered by another second-stage uplinkresource scheduling message in a determined time period prior toreception of the second-stage uplink resource scheduling message, and atransmitter, which in operation, performs the uplink transmission viathe unlicensed cell responsive to the first-stage uplink resourcescheduling message determined to be valid.
 2. The user equipmentaccording to claim 1, wherein the processor in operation, invalidatesthe first-stage uplink resource scheduling message when the uplinktransmission having has been triggered by the another second-stageuplink resource scheduling message in the determined time period.
 3. Theuser equipment according to claim 1, wherein the first-stage uplinkresource scheduling message is addressed to the user equipment, and thesecond-stage uplink resource scheduling message is commonly addressed toa plurality of user equipments receiving the second-stage uplinkresource scheduling message.
 4. The user equipment according to claim 3,wherein the first-stage uplink resource scheduling message is addressedto the user equipment by means of a user-equipment-specific identityemployed in the transmission of the first-stage uplink resourcescheduling message, and wherein the user-equipment-specific identity isconfigurable.
 5. The user equipment according to claim 3, wherein thesecond-stage uplink resource scheduling message is commonly addressed tothe plurality of user equipments receiving the second-stage uplinkresource scheduling message by means of a shared identity employed inthe transmission of the second-stage uplink resource scheduling message,wherein the shared identity is pre-defined and common to the pluralityof user equipments.
 6. The user equipment according to claim 1, whereinthe first-stage uplink resource scheduling message indicates thedetermined time period.
 7. The user equipment according to claim 1,wherein the first-stage uplink resource scheduling message furtherindicates a first time offset to be considered when performing theuplink transmission.
 8. The user equipment according to claim 7, whereinthe second-stage uplink resource scheduling message indicates a secondtime offset to be considered when performing the uplink transmission. 9.The user equipment according to claim 8, wherein the transmitter, inoperation, performs the uplink transmission at least after the sum ofthe first and second time offset upon receiving the second-stage uplinkresource scheduling message.
 10. The user equipment according to claim1, wherein the first-stage uplink resource scheduling message is adownlink control information (DCI) message of format 0A, 0B, 4A, or 4B,respectively comprising a first-stage flag indicating that the DCImessage is a first uplink resource scheduling message of a two-stagesuplink resource scheduling.
 11. The user equipment according to claim10, wherein the second-stage uplink resource scheduling message is adownlink control information (DCI) message of format 1C, comprising asecond-stage flag indicating that the DCI message is a second uplinkresource scheduling message of a two-stages uplink resource scheduling.12. A method performed by a user equipment comprising: receiving from aradio base station a first-stage uplink resource scheduling message,which indicates uplink radio resources usable by the user equipment toperform an uplink transmission via a unlicensed cell, receiving from theradio base station a second-stage uplink resource scheduling message,which is related to the first-stage uplink resource scheduling message,determining that the first-stage uplink resource scheduling message isvalid when the uplink transmission has not been triggered by anothersecond-stage uplink resource scheduling message in a determined timeperiod prior to reception of the second-stage uplink resource schedulingmessage, and performing the uplink transmission via the unlicensed cellresponsive to the first-stage uplink resource scheduling messagedetermined to be valid.
 13. The method according to claim 12, furthercomprising invalidating the first-stage uplink resource schedulingmessage when the uplink transmission has been triggered by the anothersecond-stage uplink resource scheduling message in the determined timeperiod.
 14. The method according to claim 12, wherein the first-stageuplink resource scheduling message is addressed to the user equipment,and the second-stage uplink resource scheduling message is commonlyaddressed to a plurality of user equipments receiving the second-stageuplink resource scheduling message.
 15. The method according to claim14, wherein the first-stage uplink resource scheduling message isaddressed to the user equipment by means of a user-equipment-specificidentity employed in the transmission of the first-stage uplink resourcescheduling message, and wherein the user-equipment-specific identity isconfigurable.
 16. The method according to claim 14, wherein thesecond-stage uplink resource scheduling message is commonly addressed tothe plurality of user equipments receiving the second-stage uplinkresource scheduling message by means of a shared identity employed inthe transmission of the second-stage uplink resource scheduling message,wherein the shared identity is pre-defined and common to the pluralityof user equipments.
 17. The method according to claim 12, wherein thefirst-stage uplink resource scheduling message indicates the determinedtime period.
 18. The method according to claim 12, wherein thefirst-stage uplink resource scheduling message further indicates a firsttime offset to be considered when performing the uplink transmission.19. The method according to claim 18, wherein the second-stage uplinkresource scheduling message indicates a second time offset to beconsidered when performing the uplink transmission.
 20. The methodaccording to claim 19, wherein the transmitter, in operation, performsthe uplink transmission at least after the sum of the first and secondtime offset upon receiving the second-stage uplink resource schedulingmessage.
 21. The method according to claim 12, wherein the first-stageuplink resource scheduling message is a downlink control information(DCI) message of format 0A, 0B, 4A, or 4B, respectively comprising afirst-stage flag indicating that the DCI message is a first uplinkresource scheduling message of a two-stages uplink resource scheduling.22. The method according to claim 21, wherein the second-stage uplinkresource scheduling message is a downlink control information (DCI)message of format 1C, comprising a second-stage flag indicating that theDCI message is a second uplink resource scheduling message of atwo-stages uplink resource scheduling.